Frequency resources used for wireless communication are scarce due to the proliferation of mobile phones. A technique for increasing the frequency utilization efficiency includes a Multiple Input Multiple Output (MIMO) transmission system put to practical use in Long Term Evolution (LTE) or the like. In order to further increase the frequency utilization efficiency, massive MIMO with a significantly larger number of transmitting/receiving antennas than the MIMO transmission system has been attracting attention in recent years (Patent Literature 1).
The massive MIMO performs beamforming with a two-dimensional active array antenna using several tens or more antenna elements, thereby achieving multi-user MIMO that allows for communication with users in different directions at the same time by directing beams toward the users, or terminals. The multi-user MIMO can expand the capacity by a base station directing beams toward a plurality of terminals and communicating with the plurality of terminals at the same time. The multi-user MIMO can also increase the propagation distance by narrowing the beam width and concentrating power.